1. Similarity and Transformations
7-2
Similarity and Transformations
Holt Geometry
Warm Up
Lesson Presentation
Lesson Quiz
Holt McDougal Geometry

2. Objectives
Draw and describe similarity transformations in the coordinate plane.
Use properties of similarity transformations to determine whether polygons are similar and to prove circles similar.

3. Example 1: Drawing and Describing Dilations
A. Apply the dilation D to the polygon with the given vertices. Describe the dilation.
D: (x, y) → (3x, 3y) A(1, 1), B(3, 1), C(3, 2)
dilation with center (0, 0) and scale factor 3

4. Example 1: Continued
B. Apply the dilation D to the polygon with the given vertices. Describe the dilation.
D: (x, y) →
P(–8, 4), Q(–4, 8), R(4, 4) 4 3 x, y
dilation with center (0, 0) and scale factor 3 4

5. Check It Out! Example 1
Apply the dilation D : (x, y)→
polygon with vertices D(-8, 0), E(-8, -4), and F(-4, -8). Name the coordinates of the image points. Describe the dilation.
to the 4 1 x, y
D'(-2, 0), E'(-2, -1), F'(-1, -2); dilation with center
(0, 0) and scale factor 1 4

6. Example 2 : Determining Whether Polygons are Similar
Determine whether the polygons with the given vertices are similar.
A. A(–6, -6), B(-6, 3), C(3, 3),
D(3, -6) and H(-2, -2),
J(-2, 1), K(1, 1), L(1, -2)
Yes; ABCD maps to HJKL by a dilation:
(x, y) → 1 3 x y ,

7. Example 2: Continued
B. P(2, 0), Q(2, 4), R(4, 4),
S(4, 0) and W(5, 0),
X(5, 10), Y(8, 10), Z(8, 0).
No; (x, y) → (2.5x, 2.5y) maps P to W, but not S to Z.

8. Example 2: Continued
C. A(1, 2), B(2, 2), C(1, 4) and
D(4, -6), E(6, -6), F(4, -2)
Yes; ABC maps to A’B’C’ by a translation: (x, y) → (x + 1, y - 5). Then A’B’C’ maps to DEF by a dilation: (x, y) → (2x, 2y).

9. Example 2: Continued
D. F(3, 3), G(3, 6), H(9, 3),
J(9, –3) and S(–1, 1),
T(–1, 2), U(–3, 1), V(–3, –1).
Yes; FGHJ maps to F’G’H’J’ by a reflection : (x, y) → (-x, y). Then F’G’H’J’ maps to STUV by a dilation:
(x, y) 1 3 x y ,

10. Example 3: Proving Circles Similar
A. Circle A with center (0, 0) and radius 1 is similar to circle B with center (0, 6) and radius 3.

11. Example 3: Continued
Circle A can be mapped to circle A’ by a translation: (x, y) → (x, y + 6). Circle A’ and circle B both have center (0, 6). Then circle A’ can be mapped to circle B by a dilation with center (0, 6) and scale factor 3. So circle A and circle B are similar.
B. Circle C with center (0, –3) and radius 2 is similar to circle D with center (5, 1) and radius 5.